1. Field of the Invention
The present invention relates to an apparatus and method for generating a public long code mask (PLCM) in a mobile communications system.
2. Discussion of the Related Art
Generally, in the cdma2000 communication system, a long code in forward channel is used in ciphering the forward channel and determining the location of a power control bit. Moreover, the long code in a reverse channel is used as an element for identifying each terminal. It also plays a role in reducing interference between subscriber terminals.
A long code is typically constructed with 42 bits. FIG. 1 is a block diagram of a general process of generating a long code and transmitting a signal. The long code, as shown in FIG. 1, is generated according to a 42-bit long code mask. The generated long code undergoes modulo-2 inner product by a transmission signal. The long code mask is separately generated per each channel.
The PLCM format used in the traffic channel is shown in FIG. 2 and FIG. 3. FIG. 2 is a diagram of a PLCM format for a reverse fundamental channel of which radio configuration (RC) is 1 or 2 and a reverse supplemental code channel.
FIG. 3 is a diagram representing a PLCM format for a reverse fundamental channel, a reverse supplemental channel, a reverse dedicated control channel, a forward fundamental channel, a forward supplemental code channel, a forward supplemental channel, a forward dedicated control channel, or a forward packet data channel.
Referring to FIG. 2 and FIG. 3, the PLCM format includes PLCM—37 (M36˜M0) constructed with least significant 37 bits of the PLCM. The PLCM—37 can be divided into first least significant bits (M36˜M32) and second least significant bits (M31˜M0).
A base station can inform a terminal of how to generate the second least significant bits M31˜M0 via an extended channel assignment message (ECAM). That is, if a PLCM type PLCM_TYPE in the ECAM is ‘0000’, the mobile station sets the first least significant bits M36˜M32 as ‘11000’ and generates the second least significant bits PLCM—32 by performing the following permutation of electronic serial number (ESN).
If ESN={E31, E30, E29, . . . , E2, E1, E0}, the second least significant bits PLCM—32 are {E0, E31, E22, E13, E4, E26, E17, E8, E30, E21, E12, E3, E25, E16, E7, E29, E20, E11, E2, E24, E15, E6, E28, E19, E10, E1, E23, E14, E5, E27, E18, E9}.
If the PLCM_TYPE is ‘0001’, the first least significant bits M36˜M32 is set to ‘11011’ and the second least significant bits PLCM—32 is set to PLCM—32r which is a 32-bit value received through the extended channel assignment message (ECAM). The ESN is the only identifier allocated to a terminal in the cdma2000 system and is used for call processing.
The structure of an ESN is shown in FIG. 4. The ESN is constructed with 32 bits. A manufacturer's code (MFC) is allocated to the most significant 8 bits and a serial number (SN) of the terminal, manufactured by a corresponding manufacturer, is allocated to the least significant 24 bits. A manufacturer's code is allocated to each manufacturer and is generically set up. If the number of terminals of the corresponding manufacturer exceeds the allocated SNs, a new MFC is allocated.
Meanwhile, it is expected that the 32-bits ESN will be exhausted as a result of product overflow. Hence, a new identifier for identifying a terminal is provided to replace the ESN. The new identifier is a mobile equipment identifier (MEID).
FIG. 5 is a diagram of a structure of a MEID. A MEID is constructed with 56 bits. A manufacturer's code (MFC) is allocated to most significant 32 bits and a serial number (SN) of a terminal manufactured by the corresponding manufacturer is allocated to least significant 24 bits.
In a related art method, a process for permutating the 32-bit ESN over a 42-bit PLCM is used. When using a 56-bit MEID, it is impossible to insert the MEID in the PLCM because the MEID is longer than the PLCM.
As such, when the MEID is used as the identifier for identifying a terminal instead of the ESN, the new method of generating a PLCM is needed.